Open phase detection system for power conversion system

ABSTRACT

An open phase detection system for a power conversion system includes a phase difference abnormality detection unit, an amplitude difference abnormality detection unit, and an open phase determination unit. The phase difference abnormality detection unit outputs a phase difference abnormality signal when an absolute value of a phase difference between a current flowing through a reactor and a current flowing through a capacitor is equal to or smaller than a phase threshold value. The amplitude difference abnormality detection unit outputs an amplitude difference abnormality signal when an absolute value of a value based on an amplitude difference between the current flowing through the reactor and the current flowing through the capacitor is equal to or smaller than an amplitude threshold value. The open phase determination unit outputs an open phase signal when receiving inputs of both the phase difference abnormality signal and amplitude difference abnormality signal.

FIELD

The present disclosure relates to an open phase detection system for apower conversion system.

BACKGROUND

PTL 1 discloses a power conversion system that converts DC powergenerated by a photovoltaic cell into AC power and supplies it to apower system. The power conversion system includes: an inverter thatconverts DC power into AC power; and an LC filter that reduces ripplesin the AC output of the inverter. This LC filter is a low-pass filterconstituted of a reactor (L) and a capacitor (C).

As for the AC output of an inverter, when at least one phase comes intoan open phase state (hereinafter, simply referred to as an “openphase”), it is necessary to stop the inverter. For example, PTL 2discloses an open phase detection system. According to the open phasedetection system, the output current of an inverter is detected by anoutput current detection circuit; and if the current of at least onephase is zero, it is determined to be an open phase and the inverter isstopped.

CITATION LIST Patent Literature

-   [PTL 1] JP 2019-47664 A-   [PTL 2] JP 2007-37215 A

SUMMARY Technical Problem

An open phase detection in a power conversion system in which an LCfilter is connected on an AC output side of an inverter, such as in PTL1, will be examined.

FIG. 3 is a view for explaining a current I_(INV) flowing through areactor (L) and a current I_(C) flowing through a capacitor (C) in anormal condition where an open phase does not occur. A solid line 31 isa waveform showing a current I_(INV) in a case where the powerconversion system is operating with a low output. A solid line 32 is awaveform showing a current I_(INV) in a case where the power conversionsystem is operating with a higher output than the solid line 31 (forexample, rated output). A broken line 33 is a waveform showing a currentI_(C). The phase of the current I_(C) advances the phase of the currentI_(INV) by 90°.

As shown by the solid line 32, when the power conversion system isoperating with a high output, a current flowing through a reactor (L) isvery large in comparison with a current flowing through the capacitor(C) (|I_(INV)|>>|I_(C)|). On the other hand, when an open phase occurs,a current does not flow to a power system side; and the amplitudes ofcurrents flowing through the reactor (L) and capacitor (C) become equal.Focusing on this point, it can be considered that if an amplitudedifference between the amplitude |I_(INV)| of a current flowing throughthe reactor (L) and the amplitude |I_(C)| of a current flowing throughthe capacitor (C) is detected to be nearly zero, it is determined as anopen phase.

However, in open phase detection using only current amplitudes, when apower conversion system (PCS) is in low output (a solid line 31 in FIG.3), an open phase may be erroneously detected. This is because anoperation point satisfying |I_(INV)|=|I_(C)| exists depending on adetection error of a sensor, the percent impedance (% Z) of anupper-level system, etc. For example, there may be such a case in whichthe power generation capacity of a photovoltaic cell is small due to abad weather and the PCS continues to be operated with a low output.

The present disclosure has been made in order to solve theabove-mentioned problem. It is an object of the present disclosure toprovide an open phase detection system for a power conversion system inwhich the erroneous detection of an open phase can be reduced.

Solution to Problem

In one embodiment, an open phase detection system for a power conversionsystem includes a first current detection unit, a second currentdetection unit, a phase difference abnormality detection unit, anamplitude difference abnormality detection unit, and an open phasedetermination unit. The power conversion system includes an LC filterconstituted by a reactor and a capacitor, the LC filter being connectedto an AC output terminal of an inverter.

The first current detection unit detects a current flowing through thereactor. The second current detection unit detects a current flowingthrough the capacitor. The phase difference abnormality detection unitoutputs a phase difference abnormality signal when an absolute value ofa phase difference between a current flowing through the reactor and acurrent flowing through the capacitor is equal to or smaller than aphase threshold value. The amplitude difference abnormality detectionunit outputs an amplitude difference abnormality signal when an absolutevalue of a value based on an amplitude difference between the currentflowing through the reactor and the current flowing through thecapacitor is equal to or smaller than an amplitude threshold value. Theopen phase determination unit outputs an open phase signal whenreceiving inputs of both the phase difference abnormality signal andamplitude difference abnormality signal

In another embodiment, an open phase detection system for a powerconversion system includes a first current detection unit, a secondcurrent detection unit, a phase difference abnormality detection unit,an amplitude difference abnormality detection unit, and an open phasedetermination unit. The power conversion system includes: an inverterthat has a plurality of AC output terminals; and a plurality of LCfilters each of which is constituted by a reactor and a capacitor and isconnected to each of the plurality of AC output terminals. The firstcurrent detection unit detects a current flowing through the reactor ofeach of the plurality of LC filters. The second current detection unitdetects a current flowing through the capacitor of each of the pluralityof LC filters. The phase difference abnormality detection unit outputs aphase difference abnormality signal when an absolute value of a phasedifference between a current flowing through the reactor which isconnected to one AC output terminal of the plurality of AC outputterminals and a current flowing through the capacitor which is connectedto the one AC output terminal is equal to or smaller than a phasethreshold value. The amplitude difference abnormality detection unitoutputs an amplitude difference abnormality signal when an absolutevalue of a value based on an amplitude difference between the currentflowing through the reactor which is connected to the one AC outputterminal and the current flowing through the capacitor which isconnected to the one AC output terminal is equal to or smaller than anamplitude threshold value. The open phase determination unit outputs anopen phase signal when receiving inputs of both the phase differenceabnormality signal and amplitude difference abnormality signal.

Advantageous Effects of Invention

According to present disclosure, by using both the amplitude and phaseof a current for open phase determination conditions, the accuracy ofdetecting an open phase can be improved. As a result, the erroneousdetection of an open phase can be reduced and application to anauthentication test for which a severe detection accuracy is requiredbecomes possible.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view for explaining a power conversion system in a firstembodiment of the present disclosure.

FIG. 2 is a circuit block diagram showing an open phase detection unitof a controller in the first embodiment of the present disclosure.

FIG. 3 is a view for explaining a current I_(INV) flowing through areactor (L) and a current I_(C) flowing through a capacitor (C) in anormal condition where an open phase does not occur.

FIG. 4 is a view for explaining a current _(INV) flowing through thereactor (L) and a current I_(C) flowing through the capacitor (C) in anopen phase condition.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will now be described withreference to attached drawings. It should be noted that in the drawings,identical or corresponding parts are denoted by the same referencesigns. Repeated explanation of such parts is appropriately simplified oromitted.

First Embodiment

(Power Conversion System)

FIG. 1 is a view for explaining a power conversion system in a firstembodiment of the present disclosure.

A power conversion system 1 is connected to a DC power supply 2 and apower system 3. The DC power supply 2 is, for example, a photovoltaicpower generator provided with a photovoltaic panel; a storage battery;or the like.

The power conversion system 1 converts DC power supplied from the DCpower supply 2, into AC power and supplies it to the power system 3.

The power conversion system 1 includes a smoothing capacitor 4, aninverter 5, a filter 6, and a controller 20.

The smoothing capacitor 4, which is connected between a positiveelectrode side and negative electrode side of the DC power supply 2,smooths fluctuations in an inter-terminal voltage.

The inverter 5 converts DC power from the DC power supply 2, into ACpower and outputs it to the power system 3. The inverter 5 may be eithera single phase or multiphase one. For one example, the followingdescription will be made on the assumption that the inverter 5 is athree-phase voltage inverter.

The three-phase voltage inverter has a circuit in which three legs(U-phase leg, V-phase leg, and W-phase leg) are connected in parallel.Each of the legs is constituted by connecting in series two arms in eachof which a switching element and a reflux diode are connected in reverseparallel. Each of the legs is connected in parallel between the positiveelectrode side and negative electrode side of the DC power supply 2.

The inverter 5 includes three AC output terminals 7 (U-phase AC outputterminal 7 u, V-phase AC output terminal 7 v, and W-phase AC outputterminal 7 w). The U-phase AC output terminal 7 u is connected to amiddle point of the U-phase leg. The V-phase AC output terminal 7 v isconnected to a middle point of the V-phase leg. The W-phase AC outputterminal 7 w is connected to a middle point of the W-phase leg.

The filter 6 is provided between the inverter 5 and the power system 3.The filter 6 is constituted by combining three LC filters (6 u, 6 v, 6w). The three LC filters (6 u, 6 v, 6 w) are respectively connected tothe three AC output terminals (7 u, 7 v, 7 w).

Each of the LC filters (6 u, 6 v, 6 w) is constituted of a reactor 8 anda capacitor 9. A reactor 8 u and a capacitor 9 u are provided betweenthe U-phase AC output terminal 7 u and the power system 3. A reactor 8 vand a capacitor 9 v are provided between the V-phase AC output terminal7 v and the power system 3. A reactor 8 w and a capacitor 9 w areprovided between the W-phase AC output terminal 7 w and the power system3.

Each of the LC filters (6 u, 6 v, 6 w) is a low pass filter. Each of theLC filters (6 u, 6 v, 6 w) reduces ripples generated due to theswitching of each of the switching elements of the inverter 5, by thefiltering effect of the reactor and capacitor.

(Open Phase Detection System)

An open phase detection system is constituted of a first currentdetection unit 10, a second current detection unit 11, and thecontroller 20.

The first current detection unit 10 includes a U-phase first currentdetector 10 u, a V-phase first current detector 10 v, and a W-phasefirst current detector 10 w. The first current detection unit 10 detectscurrents (I_(INV_U), I_(INV_V), I_(INV_W)) flowing through therespective reactors (8 u, 8 v, 8 w) of the three LC filters (6 u, 6 v, 6w).

The second current detection unit 11 includes a U-phase second currentdetector 11 u, a V-phase second current detector 11 v, and a W-phasesecond current detector 11 w. The second current detection unit 11detects currents (I_(C_U), I_(C_V), I_(C_W)) flowing through therespective capacitors (9 u, 9 v, 9 w) of the three LC filters (6 u, 6 v,6 w).

The controller 20 receives an input signal which includes: a powercommand according to output supply to the power system 3, which is inputfrom outside of the power conversion system 1; an output current of theinverter 5; etc. The controller 20 generates, based on the input signal,a gate signal that drives each of the switching elements of the inverter5. By the gate signal, the output power of the inverter 5 is controlledin PWM (Pulse Width Modulation).

In addition, the controller 20 includes an open phase detection unit 21.With reference to a circuit block diagram in FIG. 2, the open phasedetection unit 21 will be described.

The open phase detection unit 21 receives currents (I_(INV_U),I_(INV_V), I_(INV_W)) flowing through the reactors (8 u, 8 v, 8 w) whichare detected by the first current detection unit 10. The open phasedetection unit 21 receives currents (I_(C_U), I_(C_V), I_(C_W)) flowingthrough the capacitors (9 u, 9 v, 9 w) which are detected by the secondcurrent detection unit 11.

The open phase detection unit 21 includes: a phase differenceabnormality detection unit 22, an amplitude difference abnormalitydetection unit 23, a detection start determination unit 24, and an openphase determination unit 25.

The phase difference abnormality detection unit 22 receives inputs ofboth the phases (∠_(INV_U), ∠_(INV_V), ∠_(INV_W)) of currents eachflowing through each of the reactors (8 u, 8 v, 8 w) and the phases(Z_(C_U), Z_(C_V), Z_(C_W)) of currents each flowing through each of thecapacitors (9 u, 9 v, 9 w); and outputs a phase difference signal (phasedifference normality signal or phase difference abnormality signal).

A more concrete description will be given below. The phase differenceabnormality detection unit 22 includes an OR circuit 221, threecomparators (222 u, 222 v, 222 w), three absolute value circuits (223 u,223 v, 223 w), and three subtractors (224 u, 224 v, 224 w).

The OR circuit 221 is connected to the three comparators (222 u, 222 v,222 w). The comparator 222 u is connected to the absolute value circuit223 u. The absolute value circuit 223 u is connected to the subtractor224 u. The comparator 222 v is connected to the absolute value circuit223 v. The absolute value circuit 223 v is connected to the subtractor224 v. The comparator 222 w is connected to the absolute value circuit223 w. The absolute value circuit 223 w is connected to the subtractor224 w.

Next, abnormality detection processing for each phase by the phasedifference abnormality detection unit 22 will be described.

First, description for a U phase will be given. The subtractor 224 uoutputs a phase difference between a phase ∠_(INV_U) and a phase∠_(C_U). The absolute value circuit 223 u outputs an absolute value ofthe phase difference. The comparator 222 u outputs a phase differencesignal based on a result of comparison between the absolute value of thephase difference and a phase threshold value Tp. Specifically, thecomparator 222 u outputs a phase difference normality signal when theabsolute value of the phase difference is greater than the phasethreshold value Tp. The comparator 222 u outputs a phase differenceabnormality signal when the absolute value of the phase difference isequal to or smaller than the phase threshold value Tp. Preferably, thephase threshold value Tp is equal to or greater than 0° and equal to orsmaller than 10°.

With reference to FIG. 3 and FIG. 4, one example will be described. FIG.4 is a view for explaining a current I_(INV) flowing through the reactor(L) and a current I_(C) flowing through the capacitor (C) in an openphase condition. A solid line 41 is a waveform showing a current I_(INV)flowing through the reactor (L) in an open phase condition. A brokenline 42 is a waveform showing a current I_(C) flowing through thecapacitor (C) in an open phase condition. In the open phase condition, acurrent does not flow to a power system 3 side. Therefore, the waveformsof currents flowing through the reactor (L) and capacitor (C) have anidentical amplitude and identical phase. The phase differenceabnormality detection unit 22 outputs a phase difference abnormalitysignal when the waveforms of currents flowing through the reactor (L)and capacitor (C) have an identical phase.

For example, assume that the phase threshold value Tp is 10°. In anormal condition where an open phase does not occur, a phase differencebetween the phase of a current flowing through the reactor and the phaseof a current flowing through the capacitor is 90° (solid line 32 andbroken line 33 in FIG. 3). At this time, the absolute value of the phasedifference is greater than the phase threshold value Tp; and thecomparator 222 u outputs 0 (phase difference normality signal). On theother hand, in an open phase condition, as described above, a phasedifference between the phase of a current flowing through the reactorand the phase of a current flowing through the capacitor is almost zero(FIG. 4). At this time, the absolute value of the phase difference isequal to or smaller than the phase threshold value Tp; and thecomparator 222 u outputs 1 (phase difference abnormality signal).

Next, description for a V phase will be given. The subtractor 224 voutputs a phase difference between a phase ∠_(INV_V) and a phase∠_(C_V). The absolute value circuit 223 v outputs an absolute value ofthe phase difference. The comparator 222 v outputs a phase differencesignal based on a result of comparison between the absolute value of thephase difference and the phase threshold value Tp. Specifically, thecomparator 222 v outputs a phase difference normality signal when theabsolute value of the phase difference is greater than the phasethreshold value Tp. The comparator 222 v outputs a phase differenceabnormality signal when the absolute value of the phase difference isequal to or smaller than the phase threshold value Tp.

Next, description for a W phase will be given. The subtractor 224 woutputs a phase difference between a phase ∠_(INV_W) and a phase∠_(C_W). The absolute value circuit 223 w outputs an absolute value ofthe phase difference. The comparator 222 w outputs a phase differencesignal based on a result of comparison between the absolute value of thephase difference and the phase threshold value Tp. Specifically, thecomparator 222 w outputs a phase difference normality signal when theabsolute value of the phase difference is greater than the phasethreshold value Tp. The comparator 222 w outputs a phase differenceabnormality signal when the absolute value of the phase difference isequal to or smaller than the phase threshold value Tp.

The OR circuit 221 outputs a phase difference normality signal whenreceiving inputs of phase difference normality signals from all of thecomparators (222 u, 222 v, 222 w). On the other hand, it outputs a phasedifference abnormality signal when receiving an input of a phasedifference abnormality signal from at least one of the comparators (222u, 222 v, 222 w). That is, the OR circuit 221 outputs a phase differenceabnormality signal when an absolute value of a phase difference betweena current flowing through the reactor and a current flowing through thecapacitor is equal to or smaller than the phase threshold value Tp in atleast one of the U phase, V phase, and W phase.

The amplitude difference abnormality detection unit 23 receives inputsof both the effective values (|I_(INV_U)|/√2, |I_(INV_V)|/√2,|I_(INV_W)|/√2) of currents each flowing through each of the reactors (8u, 8 v, 8 w) and the effective values (|I_(C_U)|/√2, |I_(C_V)/√2,|I_(C_W)|/2) of currents each flowing through each of the capacitors (9u, 9 v, 9 w); and outputs an amplitude difference signal (amplitudedifference normality signal or amplitude difference abnormality signal).It should be noted that the effective value of each of the currents isan average value of an absolute value of the current in a currentwaveform for prior one cycle.

A more concrete description will be given below. The amplitudedifference abnormality detection unit 23 includes an OR circuit 231,three comparators (232 u, 232 v, 232 w), three absolute value circuits(233 u, 233 v, 233 w), and three subtractors (234 u, 234 v, 234 w).

The OR circuit 231 is connected to the three comparators (232 u, 232 v,232 w). The comparator 232 u is connected to the absolute value circuit233 u. The absolute value circuit 233 u is connected to the subtractor234 u. The comparator 232 v is connected to the absolute value circuit233 v. The absolute value circuit 233 v is connected to the subtractor234 v. The comparator 232 w is connected to the absolute value circuit233 w. The absolute value circuit 233 w is connected to the subtractor234 w.

Next, abnormality detection processing for each phase by the amplitudedifference abnormality detection unit 23 will be described.

First, description for the U phase will be given. The subtractor 234 uoutputs a current effective value difference (a value based on anamplitude difference) between a current effective value |I_(INV_U)|/√2and a current effective value |I_(C_U)|/√2. The absolute value circuit233 u outputs an absolute value of the current effective valuedifference. The comparator 232 u outputs an amplitude difference signalbased on a result of comparison between the absolute value of thecurrent effective value difference and an amplitude threshold value Ta.Specifically, the comparator 232 u outputs an amplitude differencenormality signal when the absolute value of the current effective valuedifference is greater than the amplitude threshold value Ta. Thecomparator 232 u outputs an amplitude difference abnormality signal whenthe absolute value of the current effective value difference is equal toor smaller than the amplitude threshold value Ta. Preferably, theamplitude threshold value Ta is equal to or less than 10% of theamplitude of a rated current.

With reference to FIG. 3 and FIG. 4, one example will be described. Inan open phase condition, a current does not flow to a power system 3side. Therefore, the waveforms of currents flowing through the reactor(L) and capacitor (C) have an identical amplitude and identical phase(solid line 41 and broken line 42 in FIG. 4). The amplitude differenceabnormality detection unit 23 outputs an amplitude differenceabnormality signal when the waveforms of currents flowing through thereactor (L) and capacitor (C) have an identical amplitude.

For example, assume that the amplitude threshold value Ta is 50 amperes.In a normal condition where an open phase does not occur, a currenteffective value difference between the effective value of a currentflowing through the reactor and the effective value of a current flowingthrough the capacitor is several hundred amperes (solid line 32 andbroken line 33 in FIG. 3). At this time, the absolute value of thecurrent effective value difference is greater than the amplitudethreshold Ta; and the comparator 232 u outputs 0 (amplitude differencenormality signal). On the other hand, in an open phase condition, asdescribed above, a current effective value difference between theeffective value of a current flowing through the reactor and theeffective value of a current flowing through the capacitor is almostzero (FIG. 4). At this time, the absolute value of the current effectivevalue difference is equal to or smaller than the amplitude thresholdvalue Ta; and the comparator 232 u outputs 1 (amplitude differenceabnormality signal).

Next, description for the V phase will be given. The subtractor 234 voutputs a current effective value difference (a value based on anamplitude difference) between a current effective value |I_(INV_V)|/√2and a current effective value |I_(C_V)|/√2. The absolute value circuit233 v outputs an absolute value of the current effective valuedifference. The comparator 232 v outputs an amplitude difference signalbased on a result of comparison between the absolute value of thecurrent effective value difference and the amplitude threshold value Ta.Specifically, the comparator 232 v outputs an amplitude differencenormality signal when the absolute value of the current effective valuedifference is greater than the amplitude threshold value Ta. Thecomparator 232 v outputs an amplitude difference abnormality signal whenthe absolute value of the current effective value difference is equal toor smaller than the amplitude threshold value Ta.

Next, description for a W phase will be given. The subtractor 234 woutputs a current effective value difference (a value based on anamplitude difference) between a current effective value |I_(INV_W)|/√2and a current effective value |I_(C_W)|/√2. The absolute value circuit233 w outputs an absolute value of the current effective valuedifference. The comparator 232 w outputs an amplitude difference signalbased on a result of comparison between the absolute value of thecurrent effective value difference and the amplitude threshold value Ta.Specifically, the comparator 232 w outputs an amplitude differencenormality signal when the absolute value of the current effective valuedifference is greater than the amplitude threshold value Ta. Thecomparator 232 woutputs an amplitude difference abnormality signal whenthe absolute value of the current effective value difference is equal toor smaller than the amplitude threshold value Ta.

The OR circuit 231 outputs an amplitude difference normality signal whenreceiving inputs of the amplitude difference normality signals from allof the comparators (232 u, 232 v, 232 w). On the other hand, it outputsan amplitude difference abnormality signal when receiving an input of anamplitude difference abnormality signal from at least one of thecomparators (232 u, 232 v, 232 w). That is, the OR circuit 231 outputsan amplitude difference abnormality signal when the absolute value of avalue based on an amplitude difference between a current flowing throughthe reactor and a current flowing through the capacitor is equal to orsmaller than the amplitude threshold value Ta in at least one of the Uphase, V phase, and W phase.

The detection start determination unit 24 receives inputs of theeffective values (|I_(INV_U)|/√2, |I_(INV_V)|/√2, |I_(INV_W)|/√2)(values based on amplitudes) of currents each flowing through each ofthe reactors (8 u, 8 v, 8 w); and outputs a detection start signal.

A more concrete description will be given below. The detection startdetermination unit 24 includes a comparator 242 and a maximum valuedetector 243. The comparator 242 is connected to the maximum valuedetector 243.

Next, abnormality detection start processing by the detection startdetermination unit 24 will be described. The maximum value detector 243detects the maximum value out of the effective values of currents eachflowing through each of the reactors (8 u, 8 v, 8 w).

The comparator 242 outputs a detection start signal when the maximumvalue is greater than a second amplitude threshold value Ts, that is,when there is a prescribed output. Preferably, the second amplitudethreshold value Ts is greater than the amplitude threshold value Ta.

That is, the detection start determination unit 24 outputs a detectionstart signal when a value based on the maximum amplitude of currentsflowing through the respective reactors (8 u, 8 v, 8 w) of the pluralityof LC filters (6 u, 6 v, 6 w) is greater than the second amplitudethreshold value Ts.

The detection start determination unit 24 allows abnormality detectionprocessing in the phase difference abnormality detection unit 22 andamplitude difference abnormality detection unit 23 to be started after aperiod such as the startup time of the power conversion system 1, inwhich the amplitude of an inverter current is almost the same as theamplitude of a capacitor current, has passed and its operation isstabilized.

The open phase determination unit 25 outputs an open phase signal whenreceiving inputs of: a detection start signal which is output from thedetection start determination unit 24; a phase difference abnormalitysignal which is output from the phase difference abnormality detectionunit 22; and an amplitude difference abnormality signal which is outputfrom the amplitude difference abnormality detection unit 23. That is, itoutputs an open phase signal when a state where the detection startsignal is output and, as shown in FIG. 4, a state where the waveforms ofcurrents flowing through the reactor (L) and capacitor (C) have anidentical amplitude and identical phase are set.

An alarm issuing unit (not illustrated) of the controller 20 receives aninput of an open phase signal. When receiving an input of the open phasesignal, the alarm issuing unit issues an alarm using a screen dialog,sound, lamp, etc. so as to notify an operator of the occurrence of anopen phase.

According to the above-described open phase detection system for thepower conversion system, with regard to currents flowing through thereactors and capacitors of the LC filters, both the amplitudes andphases of the currents are used for open phase determination conditionsin open phase detection and therefore, the accuracy of detecting an openphase can be improved. As a result, the erroneous detection of an openphase can be reduced and application to an authentication test for whicha severe detection accuracy is required becomes possible.

(Modification)

The open phase detection system in the first embodiment described aboveis provided with the detection start determination unit 24; however, itmay have a configuration in which the detection start determination unit24 is not included. In this case, the open phase determination unit 25outputs an open phase signal when receiving inputs of both the phasedifference abnormality signal and amplitude difference abnormalitysignal.

In addition, the open phase detection system in the first embodimentdescribed above uses a “current effective value” in the amplitudedifference abnormality detection unit 23; however, it may use the“amplitude of a current” instead of it. In this case, a “value based onan amplitude difference” is a difference between the amplitude of acurrent flowing through the reactor and the amplitude of a currentflowing through the capacitor.

Further, the open phase detection system in the first embodimentdescribed above uses a “current effective value” in the detection startdetermination unit 24; however, it may use the “amplitude of a current”instead of it. In this case, the “values based on amplitudes” are theamplitudes of currents flowing through the reactors.

Although the embodiments according to the present disclosure have beendescribed above, the present disclosure is not limited to the aboveembodiments and various modifications can be made without departing fromthe scope of the present disclosure.

REFERENCE SIGNS LIST

-   1 Power conversion system-   2 DC power supply-   3 Power system-   4 Smoothing capacitor-   5 Inverter-   6 Filter-   6 u, 6 v, 6 w LC filter-   7 AC output terminal-   7 u U-phase AC output terminal-   7 v V-phase AC output terminal-   7 w W-phase AC output terminal-   8 u, 8 v, 8 w Reactor-   9 u, 9 v, 9 w Capacitor-   10 First current detection unit-   10 u U-phase first current detector-   10 v V-phase first current detector-   10 w W-phase first current detector-   11 Second current detection unit-   11 u U-phase second current detector-   11 v V-phase second current detector-   11 w W-phase second current detector-   20 Controller-   21 Open phase detection unit-   22 Phase difference abnormality detection unit-   23 Amplitude difference abnormality detection unit-   24 Detection start determination unit-   25 Open phase determination unit-   221 OR circuit-   222 u, 222 v, 222 w Comparator-   223 u, 223 v, 223 w Absolute value circuit-   224 u, 224 v, 224 w Subtractor-   231 OR circuit-   232 u, 232 v, 232 w Comparator-   233 u, 233 v, 233 w Absolute value circuit-   234 u, 234 v, 234 w Subtractor-   242 Comparator-   243 Maximum value detector-   Tp Phase threshold value-   Ta Amplitude threshold value-   Ts Second amplitude threshold value

The invention claimed is:
 1. An open phase detection system for a powerconversion system including an LC filter constituted by a reactor and acapacitor, the LC filter being connected to an AC output terminal of aninverter; the open phase detection system comprising: a first currentdetection unit for detecting a current flowing through the reactor; asecond current detection unit for detecting a current flowing throughthe capacitor; a phase difference abnormality detection unit foroutputting a phase difference abnormality signal when an absolute valueof a phase difference between a current flowing through the reactor anda current flowing through the capacitor is equal to or smaller than aphase threshold value; an amplitude difference abnormality detectionunit for outputting an amplitude difference abnormality signal when anabsolute value of a value based on an amplitude difference between thecurrent flowing through the reactor and the current flowing through thecapacitor is equal to or smaller than an amplitude threshold value; andan open phase determination unit for outputting an open phase signalwhen receiving inputs of both the phase difference abnormality signaland amplitude difference abnormality signal.
 2. The open phase detectionsystem for the power conversion system according to claim 1, comprising:a detection start determination unit for outputting a detection startsignal when a value based on an amplitude of a current flowing throughthe reactor is greater than a second amplitude threshold value; whereinthe open phase determination unit outputs an open phase signal whenreceiving inputs of the detection start signal, the phase differenceabnormality signal, and the amplitude difference abnormality signal. 3.An open phase detection system for a power conversion system includingan inverter and a plurality of LC filters, the inverter having aplurality of AC output terminals, the LC filters each being constitutedby a reactor and a capacitor and being connected to each of theplurality of AC output terminals; the open phase detection systemcomprising: a first current detection unit for detecting a currentflowing through the reactor of each of the plurality of LC filters; asecond current detection unit for detecting a current flowing throughthe capacitor of each of the plurality of LC filters; a phase differenceabnormality detection unit for outputting a phase difference abnormalitysignal when an absolute value of a phase difference between a currentflowing through the reactor connected to one AC output terminal of theplurality of AC output terminals and a current flowing through thecapacitor connected to the one AC output terminal is equal to or smallerthan a phase threshold value; an amplitude difference abnormalitydetection unit for outputting an amplitude difference abnormality signalwhen an absolute value of a value based on an amplitude differencebetween the current flowing through the reactor connected to the one ACoutput terminal and the current flowing through the capacitor connectedto the one AC output terminal is equal to or smaller than an amplitudethreshold value; and an open phase determination unit for outputting anopen phase signal when receiving inputs of both the phase differenceabnormality signal and the amplitude difference abnormality signal. 4.The open phase detection system for the power conversion systemaccording to claim 3, comprising: a detection start determination unitfor outputting a detection start signal when a value based on a maximumamplitude of currents each flowing through the reactor of each of theplurality of LC filters is greater than a second amplitude thresholdvalue; wherein the open phase determination unit outputs an open phasesignal when receiving inputs of the detection start signal, the phasedifference abnormality signal, and the amplitude difference abnormalitysignal.
 5. The open phase detection system for the power conversionsystem according to claim 4, wherein the second amplitude thresholdvalue is greater than the amplitude threshold value.
 6. The open phasedetection system for the power conversion system according to claim 3,wherein the phase threshold value is equal to or greater than 0° andequal to or smaller than 10°.
 7. The open phase detection system for thepower conversion system according to claim 3, wherein the amplitudethreshold value is equal to or smaller than 10% of an amplitude of arated current.